Telephone



R. L. MURRAY.

TELEPHONE.

APPLICATION FILED SEPT. 16, I920.

1,412,539. Patented Apr. 11, 1922.

UNITED STATES PATENT OFFICE.

ROBERT LAMBERT MURRAY, 01 BUSHEY HEATH, ENGLAND, ASSIGNOB TO THE TELE-PHONE MANUFACTURING COMPANY, (1920) LIMITED, OF LONDON, ENGLAND, ABRITISH LIMITED LIABILITY COMPANY;

TELEPHONE.

Specification of Letters Patent.

Patented .Apr. 11, 1922.

To all whom it may concern:

Be it known that I, ROBERT LAMBERT MURRAY, a subject of the KinIgI ofEngland, residing in Bushey Heath, ertfordshire, England, have inventedcertain new and useful Improvements in Telephones, of which thefollowing is a specification;

This invention relates to telephones-and in particular to a receiver andtransmitter secured together as an unitary device somewhat after themanner of what are known as hand-combinations.

The term hand-combination is hereinafter employed to denote anyconstruction in which a users transmitter and receiver are securedtogether as an unitary structure, whether or no it is to. be held in theusers hand.

One object, and-the principal object, of this invention, is to reducethe loudness of what are known as sidetones, and particularly inhand-combinations whereof the transmitter is to be held against theusers throat.

In back-to-back hand-combinations known heretofore it has beenconsidered necessary to employ between the transmitter, and re ceiver afilling material to act as a damper to prevent the phenomenon known ashowling. We have found that such damper can be dispensed with when themicrophone and receiver, whereof the resistances are in a pre-determinedratio one to the other, are

directly connected in parallel with one another, and the microphone andreceiver can therefore be both directly secured, with obviousadvantages, on a rigid metallic mounting extending between the same. Ithas heretofore been known to connect a transmitter and receiver at astation in parallel with one another for use with a common battery; inone such known arrangement an induction coil had its primary windingconnected in series with the microphone and its secondary winding inseries wit the receiver. By dispensing with the use 'of an inductioncoil the construction is still further simplified and the cost ofmanufacture reduced.

According to the present invention, therefore, a telephonehand-combination has its microphone and-receiver connected directly inparallel with one another, and the points of electrical junction of thesaid two parts are connected directly to the transmission lines, for thepurpose of reducing side-tones.

Preferably, the at-rest resistance of the microphone and that of thereceiver at a station are approximately in the ratio of 2 :1.

According to another feature of the invention, a telephonehand-combination wherein the microphone and receiver are mountedback-to-back on a support common to them both and are connectedelectrically in parallel with one another when operated, ischaracterized by the support being in the form of a rigid metallicmounting extending between and directly secured to the microphone andreceiver.

Conveniently, a telephone hand-combination having its microphone andreceiver connected as described above is arranged for common batteryoperation and in such a manner that the said battery always tends tostrengthen the permanent magnetism of the receivers.

The accompanying drawings illustrate a construction of divers telephoneembodying this invention,

Figure 1- being a perspective view of a transmitter and receiverarranged as a handcombination Figure 2 being a central vertical sectionthrough the instrument on the line 22 of Figure 3;

Figure 3a front elevation with the receiver.

diaphragm and itsjcap removed, and

Figure 4 a diagram of the circuits.

Dealing first with the arrangement of the circuits, they are so arrangedthat the receiver R and transmitter T are at one station connected inparallel with one another and through the lines L-L to the transmitter Tand receiver R at the other station which transmitter, and receiver areagain in parallel with one another.

Dealing with the actual construction shown in Figures 1-3, a cup-shapedfoundation A is provided, screw-threaded externally at A to engage thereceiver-cap B and at A to enga e the transmitter-cap. C. The receiverdiap 'ragm is indicated at B and the transmitter diaphragm at C, eachbeing clamped in position by its res ctive cap, the diaphragm B.directly to t e upstanding wall A of the foundation and the diaphragm Cby means of a loose mg C interposed between the cap C and the bottom ofthe foundation A.

On the right-hand-side of,the bottom of the foundation, as viewed inFigure 2, is mounted the microphone D, and on the lefthand side theieceiver magnets seen at E. These magnets are each in the form of asemi-circle and are held in position with their similar poles opposingone another and in very close proximity to one another, each pole beingprovided with a slight semi-circular groove to accommodate the stem of afixing screw E One of these fixing screws further serves, by means of alug F to hold the outer pole-piece in the form of a ring F in position,while the other holds a core, concentric with the ring F, in position,by means of a lug G. The core is not seen in the drawing bein surroundedby the usual operating coil i A'curved plate spring H isprovided on theinner face of the wall A so as to constitute a spring key for which achin-push H is provided. One end of the spring is secured by screws tothe wall'A and the other end is free to be operated by the push H andmake contact atH with a contact plate held between blocks H ofinsulating material against the wall A The usual three flexible leads J,J, J? are brought in through the wall A at a point opposite the push Hand are connected in any convenient manner to their appropriate parts ofthe" device so as to constitute a ringing and speaking circuit in theusual well-known manner. As shown in Figure 4 a one-way ringing circuitcomprising a bell X is provided.

On the outside of the cap B of the receiver, which cap serves totally toenclose the diaphragm B, there is mounted a connector K communicating bya central perforation K with the space between the inside of the cap andthe diaphragm B, and by means of lateral perforated branches K withflexible tubes, not shown in the drawing, serving to conduct the soundto the users ears.

A strap M is provided to enable the device to be secured to the usersneck so as to present the cap C to the throat in the neighbourhood ofthe larynx and so that the user can readily depress the push H with hischain.-

In connecting the apparatus up care is to be taken that the battery Zand the coils G are so interconnected that the effect of the battery isalways to tend to strengthen the permanent magnets of the receivers.

Contrary to what might be expected, it is found with the apparatusconstructed and connected in the manner just above described, the nseris not troubled with what are ordinarily known as side-tones, in spiteof the fact that the transmitter is mounted directly upon the receiver.The coil G and the microphone Dare constructed to have resistance valuessuch as are ordinarily employed for telephonic communication overreasonable distances for diving operations and the like, and by means ofordinary line wires 01' cables. For example, the receiver coil may havea valueof- 15 ohms and the transmitter an at-iest resistance of 25 ohms.The instrument as thus constructed does not howl and it is believed thatcontributary causes to this satisfactory result are to be found in theexistence of the solid bottom A of the foundation between the receiverand transmitter, and, in an even more important degree, tothe'arrangement indicated in Figure 4. It will readily be-u'nderstpodthat variations inthe transmitter resistance will not, when the partsare arranged in par allel as shown, act so directly-upon the receiver aswhen they are connected in series in the usual manner. It is well-knownwith the receiver and transmitter in series with one another as isusual, a telephone may be made to howl, as it is called, by holding thereceiver opposite to the transmitter and the tendency to do this hasheretofore militated against success of instruments in which thereceiver and transmitter were mounted in very close proximity to oneanother and each'mechanically supporting the other.

What I claim as my invention and desire to secure by Letters Patent is'1. In a telephone system between two sta-r tions the combination of atransmitter and a receiver at one station mounted back to back upon asupport common to them both, connections connecting the receiver andtransmitter directly in parallel with one another, a'receiver andtransmitter at the other station mounted and connected in relation toone another as are those at the first said station, aspeech-transmitting conductor connected at one end directly to one pointof electrical junction between receiver and transmitter at one stationand at the other end directly to the point of junction betweentransmitter and receiver at the other station, a battery and a secondspeech-transmitting conductor connected at one end directly to thesecond point of junction between transmitter and receiver at one stationand through sald battery to the second point of junction betweentransmitter and receiver at the other station, substantially as setforth.

. 2. In a telephone system between two stations the combination of atransmitter and a receiver at one station mounted back to back upon asupport common to them both,

the receiver, a receiver and transmitter at the other station mountedand connected in relation to one another as are those at the first saidstation, and whereof the at-rest.

resistance of the microphone is approximately double that of thereceiver, a transmitting conductor connected at one end directly to onepoint of electrical junction between receiver and transmitter at onestation and atthe other end directly to the point of junction betweentransmitter and receiver at the other station, a battery and a secondtransmitting conductor connected at one end directly to the second pointof junction between transmitter and receiver at one station and throughsaid battery to the second point of junction between transmittel' andreceiver at the other station, substantially as set forth.

- 3. In a telephone system between two sta' tions the combination ofatransmitter and a receiver at one station mounted back to back upon asupport common to them both, connections connecting the receiver andtransmitter directly in parallel with one another, a receiver andtransmitter. at the other station mounted -and connected in relation toone another as are those at the first said station, a transmittingconductor connected at. one end directly to one point of electricaljunction between receiver and transmitter at one station and at theother end directly to the point of junction between transmitter andreceiver at the other station, a battery and a second transmittingconductor connected at one end directly to the second point of junctionbetween transmitter and receiver at one station and through said batteryto the second point of junction between transmitter and receiver at theother station in such a manner that the said battery tends always tostrengthen the permanent magnetism of the said two receivers,substantially as set forth.

4;. In a telephone system between two stations the combination of 'atransmitter and a receiver at one station mounted back-toback on asupport common to them both and connected directly in parallel with oneanother, a flexible tie extending between two points of attachmenttherefor to the said support for the purpose described, a bellpushprojectin radially outwards from the said support For the purposedescribed, a receiver and transmitter at the other station connecteddirectly in parallel with one another, a transmitting conductorconnected at one end directly to one point of electrical junctionbetween receiver and transmitter at one station and at the other enddirectly to the point of junction between transmitter and receiver atthe other station, a battery 'and a second transmitting conductorconnected at one end directly to the second point of junction betweentransmitter and receiver atone station and through said battery to thesecond point of junction between transmitter and receiver at the otherstation, a calling circuit comprising a line wire and a calling devicein series with one another whereof one end is connec'ted to theaforesaid bell-push and the other end is connected to the point ofjunction between the transmitter and receiver at the said secondstation, substantiall as set forth.

In testimony whereofi aflix m si nature.

ROBERT LAMBERT M R AY.

